1. Field of the Invention
This invention relates to a composite guide mechanism for machine tools, and more particularly to a guideway mechanism in which one of a pair of opposed guideways is formed into a hydrodynamic guideway and the other guideway is formed into a hydrostatic guideway.
2. Description of the Prior Art
In a conventional vertical guide mechanism which is formed into a pair of opposed hydrodynamic guideways, the momental external force acts on its moving body, and so the moving body inclines with respect to its guideways and a non-uniform contact pressure distribution generates in the guideways, so that the moving body partially contacts with the guideway in a non-uniform state, because the clearance exists between guideway and moving body. In an extreme case, both the metals mutually contact to each other, so that the wear thereof is accelerated.
Furthermore, in a conventional guide mechanism, two opposed master guides exist in guideways, and either of the guideways becomes a master guide depending upon the external force which functions onto the moving body. In this case, since the master guide is not constant, an unstable motion of the moving body occurs, so that it has been difficult to effect the precise positioning.
Moreover, when a conventional opposed guideway mechanism is compared with an opposed hydrostatic guideway, the former mechanism has a smaller frictional force, so that disadvantageous phenomena such as one-sided contact and the like are difficult to occur. In this case, however, since the frictional force is small, the effects for controlling vibration due to friction cannot absolutely be expected. Besides the above facts, the opposed guideway mechanism receives substantially the external force being applied to the moving body by means of the driving system, and as a consequence, the moving body is unnecessarily displaced, so that precision of the positioning has deteriorated.